Firstly, if you are happy with that layout I would put the mech vario on the left, ASI on the right the altimeter below. Then you have the LCD Vario close to the mechanical and the 5000. ASI and Varios are used the most.

My personal preference would be the LCD vario cente top, the 3x 80mm below (5000 ASI and mechanical vario) then altimeter below that. I would leave a suitable space for a panel mounted radio- bear in mind these can be reasonably long and heavy!). Compass can either be put on one of the extremes, at the top with the LCD vario or on the bottomStalk- it rarely gets used as you have a GPS!

Is this more in line with what you are thinking? I don't think this panel was designed for this many instruments, so the mounts are in awkward places. To try and leave room for the radio, do you think it would be better to try and put the compass further down on the stem, or just try to squeeze everything further up and outwards?

Tricky, the 2 outer 80mm could maybe move up slightly to give more room on the edges- or swap the 5000 with the top 2 57mm? There will be plenty of room for a PDA on a gooseneck mount. What you have done in the 2nd pic is what I had in mind- as the arch isn't very pronounced on top seems better to put 2x 57mm or maybe 1x 80mm at the top rather than one. A 57mm radio looks like it could then go on the left side or the bottom stalk.

We do have a radio. It will be interesting fitting it, but the plan is to try to mount it onto the stalk of the panel. I don't know the dimensions for it so at the moment I am simply leaving the space clear.

Is there any chance that a standard compass, like the one we have, is smaller than 57 mm? That template was just a guess. If it is smaller than 57 then it might make things easier.

What do you all think about this combination? I found that if I move the compass down onto the stem, that the empty space in the middle is actually big enough to fit another 80mm circle. I was thinking that this could be a good place to mount the radio.

Do you think that the spaces around these instruments will be large enough to accommodate the stuff behind the panel?